Charge pump circuits are used to source current to or sink current from a load in response to control signals. Typically, these control signals consist of an UP signal and a DOWN signal. Current is sourced to the load in a case that the UP signal is active and the DOWN signal is inactive, and current is sunk from the load in a case that the UP signal is inactive and the DOWN signal is active. Ideally, no current flows through the load if both control signals are in the same state.
In a non-ideal charge pump, some current flows to or from the load if both control signals are in the same state. This current is known as leakage current. A charge pump is often designed in view of a maximum allowable leakage current specified by applicable charge pump design specifications.
Leakage current affects the output swing of a charge pump. More particularly, output swing is defined as the maximum swing at the output of a charge pump which results in a leakage current that is less than the specified maximum allowable leakage current. Some applications require charge pumps having one or more of a high output swing, a high output impedance, a stable common-mode output, and low voltage headroom requirements.